1. Field of the Invention
This invention relates to an improved method and apparatus for the mass rearing of insects, particularly fruit flies.
2. Description of the Art
Tephritid fruit flies (Diptera: Tephritidae) such as the Mediterranean fruit fly [Ceratitis capitata (Wiedemann)] commonly known as the medfly, the oriental fruit fly (Dacus dorsalis Hendel), the melon fly (Dacus cucurbitae Coquillett), the Caribbean fruit fly [Anastrepha suspensa (Loew)], the olive fruit fly (D. oleae Gmelin), and the Mexican fruit fly [A. ludens (Loew)] are among the worst pests of citrus, deciduous fruits, and vegetables and present a major threat to fruit and vegetable production in areas with mild winters.
Currently, the primary method of control of fruit flies is the extensive use of insecticides or insecticidal baits. The widespread broadcasting of insecticides has several disadvantages, notably, the development of insecticide resistance, the destruction of bees and desirable predators and parasites, and contamination of the environment. One alternative method of control is the release of large numbers of sterile male fruit flies which mate with the native female population resulting in the production of infertile eggs.
An important factor in the success of any sterile-insect release program is the ability to efficiently and economically mass produce the flies. The first step in the mass production of sterile Mediterranean fruit flies is the production of eggs. The most commonly used collection technique is the screen method. In this method a large cage having a synthetic cloth front screen panel is mounted on a monorail. The fruit flies are placed inside the cage in the pupal stage and when they emerge, they oviposit through the screen and the eggs drop into a trough of water located on the outside of the cage. The water prevents desiccation of the eggs. The screen method has been adapted most successfully at the Mediterranean Fruit Fly Mass Rearing Facility, Metapa, Mexico, to collect over one billion eggs per week. The primary disadvantage of this method is that many of the eggs get caught on the screen and desiccate completely or partially prior to dropping into the trough. Thus the viability and quality of the eggs are significantly reduced.
A second method of egg collection is oviposition into perforated polyethylene bottles held in openings in a cage. Subsequent to oviposition by the flies, the bottles are removed from the cages for collection of the eggs. The bottle method has been used primarily as a research tool and was first used on a large scale (over 200 million eggs per week) in 1980 for the California medfly infestation at the California/APHIS Mediterranean fruit fly facility in Honolulu. At this facility, about 120,000 adult flies are housed in cages (41.times.117.times.107 cm) made of 0.95-cm plywood with mesh screening at the top. Two circular openings are located on each side of a cage to receive opaque 1-liter, slightly tapered, cylindrical polyethylene, capped bottle containers having 300 holes (denoted as 0.3-mm diameter). A cellulose sponge saturated with water or fruit juice is placed in the container to provide ovipositional stimulus and prevent desiccation of the eggs. The flies oviposit through the holes into the bottles. The primary disadvantage of this method is the time consuming and labor intensive egg collection procedure which involves removing each container from the cage, uncapping the container, and washing out the eggs. Another disadvantage is the escape of flies from the cage when the containers are removed. A third disadvantage is the lack of amenability of this system to automation. The hundreds of bottles needed for collection of over 200 million eggs precludes both the use and automation of the bottle system for egg collection in a large scale mass production facility (over 1 billion eggs per week).